commander_47

1974, LS4, 454

I'm going over the heat riser and am torn about removing the vane. The vane would have to be cut off as it is spot welded on.

By removing just the vane the dual exhaust will work normally, looks original and the top end won't ever overheat.

Bikespace

What are you torn about? Cut the whole shaft out, and plug the holes.

You can also buy a replacement "spacer" that does exactly this.

427SIXPACK

Reason ?

69L88

Buy the spacer and put the riser on the shelf unless you are planning to enter NCRS judging events.

Faster Rat

You could always just put a small tack weld in the.open position

Jebbysan

Even wide open the flap is a pretty good deterrent to flow......cut it out or get the mentioned spacer......

Jebby

Hopper12

On our '68 L71 I decided to get rid of the vane, but leave it stock looking. A few minutes with a cutting disk on my dremel and good to go. No one would ever know, and I don't need it.

Mdbirk

I used this exact one on my 68 big block. https://www.ebay.com/itm/22528942019...SABEgIl1PD_BwE

commander_47

Thanks to all who replied.

I just couldn't see any good reason for throwing this in a box until I die.

So I cut it out and simply welded up the holes.

Still looks original.

C3Highway

The heat riser is designed to more quickly warm up your intake manifold and carb to ease cold starts. With it functioning properly your carb will certainly utilize less choke and therefore run rich for a shorter period of time during each and every cold start. The colder the engine is, the greater the benefit. The warmer it is, the less advantage is realized.

In a sense, the heat riser does for your intake and carb what your engine thermostat does for your engine block and heads.

The Early Fuel Evaporation (EFE) system aids with vaporization of fuel in cold conditions, as well as to reduce exhaust emissions. However, heat risers were originally installed on cars solely for warming up the carb, not for emissions related concerns. Those concerns came decades later, as it became clear that warm engines run cleaner then cold engines.

The primary component in the EFE system in question is a vacuum actuated Heat Riser mounted below the right-side exhaust manifold.

Noteworthy, is Chevy designed the EFE system so that in the event of a vacuum failure, the heat riser will fail wide open. That was a good idea.

Nevertheless, that leaves the possibility of a mechanical failure of the heat riser (becomes stuck in the closed position), which can happen, and that would cause the engine to struggle at higher RPM. Not good. Therefore, if that were to happen, replace the failed heat riser, like any other failed exhaust part on the car that provides a benefit.

In the meantime, with a functioning EFE system, the C3 will run better sooner over thousands of cold startups. This is especially true for all those times it is cold or very cold out.​

commander_47

[QUOTE=Noteworthy, is Chevy designed the EFE system so that in the event of a vacuum failure, the heat riser will fail wide open. That was a good idea.

Nevertheless, that leaves the possibility of a mechanical failure of the heat riser (becomes stuck in the closed position), which can happen, and that would cause the engine to struggle at higher RPM. Not good. Therefore, if that were to happen, replace the failed heat riser, like any other failed exhaust part on the car that provides a benefit.

.​[/QUOTE]


My Corvette heat riser on the exhaust flange is not run off a vacuum. It is controlled by the bi-metal spring. Just like on the choke. As the spring gets hot, it expands and pulls the vane open and holds it there as long as its hot.

As you can see in the pic above, my heat riser is rusted and played out. It was working but creaking and and the little stop pin is about to fall off. No matter how much WD 40 won't help. It will just burn off as soon as the car is run.

I believe the fail safe is the counterweight you see in the pic. If the spring breaks, then the counterweight is supposed to hold the vane open all the time. If the vane is so rusty it barely moves, then it could easily stick closed or partially closed.

I'm so **** I just don't want to worry about it.

Cam33

it’s there for a reason . Fix it and leave it alone

Bikespace

427SIXPACK